The present invention generally relates to an apparatus for preparing at least one tooth for receiving a crown, bridge and the like. The tooth is prepared using a mould model at least including one model tooth. Crowns and bridges and other dental elements are used for the reconstruction of defect teeth and of gaps between teeth in human sets of teeth. A crown is used in combination with a single tooth, and a bridge is used to expend over a plurality of teeth.
It is generally known in the art to reconstruct a tooth with a crown as follows:
The dentist first prepares the tooth to be reconstructed by grinding the tooth until a stub is received. Material of the tooth is removed to attain enough room for the crown. Grinding a tooth to form a stub requires substantial skills and concentration. Grinding is conducted by the dentist and in the mouth of the patient. Consequently, it is sometimes hard to correctly see the tooth, and reactions of the patient lower the quality of the preparation result. The required time for preparation is also influenced by the mouth anatomy, for example by adjacent teeth. After having prepared the tooth to form a tooth stub, a mould is produced in the mouth of the patient to attain a negative form corresponding to the tooth stub. The mould is then filled with plaster in a laboratory. Consequently, one attains a positive model, meaning a model tooth made of plaster. A technical crown is produced on this model tooth stub. The crown will be later placed upon the tooth stub, and it will be connected thereto using cement or different connection means. The exactness attainable with this known method is limited. Usually, extra work in the mouth of the patient is required. Especially, there may be problems in the region of the rim of the crown, meaning at the place where the crown closely contacts the natural tooth material.
A method of patient specific manufacture of and treatment with dental prosthetic work pieces is known from German Patent No. 44 43 921 C1 corresponding to European Patent No. 0 796 063 B1 and International Application PCT/EP95/04764 published under WO 96/17561. The method involves, first, taking an initial impression of the jaw to be treated including the checkbite in the mouth without earlier preparation steps. Then, a positive mould model of the jaw is produced followed by grinding of the mould model. The model in the resulting state is then stored by optical and/or mechanical scanning of the geometrical configuration of the mould model. Then, exclusively using the mould model, a crown or a bridge is produced in the known way. In the following, it is necessary to grind the natural tooth in the jaw of the patient using the stored data of the mould model, and to insert the crown or the bridge. In the known method, it is unclear in which way it is desired to attain a relation between the mould model and the tooth in the jaw of the patient. It is also unclear in which way the required intra oral milling unit is to be anchored and positioned, respectively, in the mouth of the patient.
The present invention relates to an apparatus for preparing at least one tooth for receiving a dental element such as a crown, bridge and the like using a mould model at least including one model tooth. The apparatus includes at least one positioning body, at least one parallelizing body, at least one mould spoon including threaded sockets and removable segments, at least one preparation base bar including sliding elements, at least one tub, at least one transmitting unit, at least one transport arm mechanism, at least one unit including position stabilizing arms, a plurality of model transfer bodies, and at least one copying grinding unit.
The present invention also relates to an apparatus for preparing at least one human tooth for receiving a dental element using a mould model at least including one model tooth. The apparatus includes at least one positioning body being designed to be inserted into an impression of a tooth to be prepared, a mould spoon including a spoon base and a plurality of segments and being designed to produce a mould model including at least one model tooth being designed to be connected to the positioning body, the segments being designed to be filled with a hardenable mass and being designed and arranged to be separately removable from the spoon base, the spoon base including a plurality of threaded sockets, at least one parallelizing body being designed to be placed upon the positioning body being connected to the model tooth to define a preparation axis, at least one preparation base bar being designed to be connected to the threaded sockets and including sliding elements, at least one transmitting unit being designed to be placed upon the parallelizing body and on the preparation base bar to transfer a reference plane perpendicular to the preparation axis to the preparation base bar, at least one tub being designed to be arranged on one of the threaded sockets to be filled with a hardenable mass, at least one transport arm mechanism being designed to be placed upon the transmitting unit and to align the plane of the preparation base bar to be parallel to the reference plane, at least one unit including position stabilizing arms and being designed to be placed upon the sliding elements, a plurality of model transfer bodies being designed to transmit a copying model of the prepared mould model to the mould spoon with positional accuracy, and at least one copying grinding unit being designed to grind the at least one tooth to be prepared scanning the copying model.
The present invention also relates to a mould spoon for producing a mould model of at least one human tooth to be prepared for receiving an dental element. The mould spoon includes a spoon base and a plurality of segments being connected to the spoon base, being filled with an impression mass, being designed to take an impression of the least one human tooth to be prepared and being designed and arranged to be separately removable from the spoon base.
The novel apparatus includes a plurality of elements and units. These elements and units are coordinated in a way to determine a preparation axis and a reference plane being located to be perpendicular with respect to the preparation axis. The elements and units of the novel apparatus are positioned and aligned in the reference plane and with respect to the reference plane, respectively. In this way, there is a family of parallel planes all being parallel with respect to the reference plane. The directions in these parallel planes are respectively maintained and transmitted to attain mutual orientation and to find, determine and find again the places at which process steps are to be conducted in an exact way. With the novel apparatus, it is possible to conduct most of the process steps outside of the mouth of the patient. Consequently, those process steps may be conducted at greater exactness and without negative influences by the patient.
The novel system includes a positioning body and an associated parallelizing body for each natural tooth. A common mould spoon or cast spoon with a mould base forms the base for this process. The preparation base bar and the sliding elements placed thereon are aligned and fixed to be parallel with respect to the reference plane. A tub serves to receive a copying model also being fixed in the tub with respect to the reference plane. A transmitting unit, a transport arm mechanism and at least one unit including position stabilizing arms for each tooth to be prepared serve to transmit the different parallel planes. Furthermore, the novel apparatus includes model transfer bodies to support the copying model at an exact position with respect to the preparation model at the mould spoon. Furthermore, the novel apparatus includes a copying grinding unit being designed and arranged to prepare the natural teeth, the copying model being used as a template. Exact positioning between the copying model and the natural teeth is important to this process. With the novel apparatus, it is possible to design, handle and insert crowns, bridges and other technical tooth portions at great exactness.
The novel apparatus has many advantages. Since the model teeth are shaped outside of the mouth of the patient without influences by the patient, the maximum attainable exactness of the crown and of the bridge, respectively, is substantially increased compared to the prior art. Mispreparation effects, as undercuts and divergences (in bridges) result in irrecoverable losses of tooth substance when preparing in situ. The novel method conducted with the novel apparatus limits the loss of tooth substance to the required minimum. Consequently, stability and biological resistance properties of the tooth stub are increased. The design of the model crown rim is more exact due to controlled preparation. This also applies to the crown rim close to the natural tooth. The crown and the bridge, respectively, attains an aligned seat at the stub of the natural tooth. Consequently, caries occurring in the annular gap in the region of the rim is minimized. The usable times of the crown in the mouth are increased. Consequently, the cost for treatment of the patient is reduced. When using the novel apparatus, it is possible to conduct most of the process steps outside of the mouth of the patient resulting in increased precision and shortened necessary process times. Additionally, stress occurring during the treatment of the patient is also reduced both for the patient and for the dentist.
The positioning body preferably has an unround bottom plate and an upper part including an outer thread. The positioning body preferably in the region of its upper part has a comparatively smaller diameter. Preferably, the positioning body is designed to be made of one piece, but it may also be made of a plurality of elements. The unround cross section of the bottom plate may be realized in different ways. It is especially simple to design the bottom plate to have a cylindrical shape, and to produce a flattened portion being arranged at one side. This flattened portion serves to insert, remove and put the positioning body back into a respective impression in the natural tooth in a way to prevent unintentional rotation. The upper part including an outer thread serves for the connection to a parallelizing body. The parallelizing body is designed and arranged to be rotatable with respect to the positioning body about ball surfaces. In this way, it is possible to define a preparation axis which is chosen to be located at the best place. With this preparation axis, one defines a reference plane which is of great importance for all process steps, and which serves as reference for each process step.
The mould spoon or cast spoon is designed as a special mould spoon. As other mould spoons, it also includes a receiving space for receiving mould mass. However, the novel mould spoon has some special features. The novel mould spoon includes a spoon base having a protruding rim on which the thread sockets are arranged in a spaced apart manner. The segments forming a spoon housing are designed and arranged to be removable from the spoon base, and they may be placed back on the spoon base. The removable segments allow for processing a mould model exactly at the place where the natural teeth to be prepared require this. During most of the process steps, the mould spoon remains at its position at the mould model. It is not only a base for the impression, but also for all process steps to be taken at the mould model. Furthermore, the mould spoon serves to finally conduct process steps in the mouth of the patient, especially for copy grinding of the natural teeth. The mould spoon realizes the necessary relationship with respect to geometry.
The parallelizing body is used in combination with the positioning body. The parallelizing body includes a screwing piece including an inner thread, a connection piece, a ball and an axis screw, the screwing piece and the connection piece connecting each other by ball surfaces. The ball surfaces allow for an three-dimensional adjustment of the angle in space, and therefore for determining the preparation axis and the reference plane. At the same time, the parallelizing bodies in combination with a transmitting unit make it possible to transmit the preparation axis from one model tooth to another model tooth. This is necessary to operate in one common reference plane. This is especially important for inserting bridges and other technical elements which span a plurality of natural teeth and/or gaps between teeth.
The transmitting unit includes a base plate which forms a reference plane. The base plate includes a bush arranged perpendicular thereto and a sliding bush for determining and transmitting a preparation axis. The base plate with its plane forms the reference plane. The perpendicular position of the reference plane with respect to the preparation axis is realized by the bush being fixedly arranged on the base plate. The sliding bush is arranged to be movable at least in one direction in the plane of the base plate. The axes of the bush and of the sliding bush are located to be parallel with respect to each other. In this way, it is possible to transmit the preparation axis from a first model tooth to a second model tooth in parallel association.
The transmitting unit further serves to align a preparation base bar with a transport arm mechanism. The preparation base bar is aligned and determined to be parallel to the reference plane by an aligning frame. The association is realized by the mould spoon. With respect to meeting the correct angle association, the base plate includes a male protrusion having an unround circumferential surface. The male protrusion cooperates with a female protrusion having a respective unround circumferential surface and being located at the transport arm mechanism. Furthermore, there is such a connection between the transport arm mechanism and the preparation base bar.
The preparation base bar includes a base body, a fixing body, a fixing screw, a saddle head and a ball for determining the preparation axis, as well as an alignment frame for receiving the sliding members. The sliding members are designed and arranged to be movable on the alignment frame. They are moved in a plane parallel to the reference plane, and in a direction parallel to a direction connecting the preparation axes of the model teeth. The saddle head in combination with a ball and a fixing screw serves to determine the position of the preparation base bar in a plane parallel to the reference plane. The number of slide members corresponds to the number of natural teeth to be prepared and to possible gaps between teeth. When desired, the number of sliding members on the aligning frame may be varied.
The transport arm mechanism and/or the unit including the position stabilizing arms are designed to transmit parallel planes keeping the preparation axis. The transport arm mechanism and the unit including the position stabilizing arms have very similar designs, and a plurality of them may be included in the novel apparatus.
Furthermore, there is a model transfer body and a copying grinding unit. The model transfer body includes a pin foot element having an unround cross section and an unround head including a calibrating impression. The model transfer body serves to transmit a copying model of the preparation model to the mould spoon in an exact way and exactly at the right position. A tub with a hardenable mass is used, the tub being arranged on the spoon base. The tub is designed to be placed on a threaded socket of the mould spoon.
Other features and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and the detailed description. It is intended that all such additional features and advantages be included herein within the scope of the present invention, as defined by the claims.